Repaint selection when element with ::selection style is recalculated.

third_party/WebKit/Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved.
  *               (http://www.torchmobile.com/)
@@ skipping 1694 matching lines @@
     else
       setNeedsLayoutAndPrefWidthsRecalc(LayoutInvalidationReason::StyleChange);
   }
 
   if (diff.needsPaintInvalidationSubtree() ||
       updatedDiff.needsPaintInvalidationSubtree())
     setShouldDoFullPaintInvalidationIncludingNonCompositingDescendants();
   else if (diff.needsPaintInvalidationObject() ||
            updatedDiff.needsPaintInvalidationObject())
     setShouldDoFullPaintInvalidation();
+  else if (diff.needsPaintInvalidationSelection())
+    invalidatePaintForSelection();
 
   // Text nodes share style with their parents but the paint properties don't
   // apply to them, hence the !isText() check.
   if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled() && !isText() &&
       (diff.transformChanged() || diff.opacityChanged() ||
        diff.zIndexChanged() || diff.filterChanged() ||
        diff.backdropFilterChanged() || diff.cssClipChanged())) {
     setNeedsPaintPropertyUpdate();
 
     // We don't need to invalidate paint of objects on SPv2 when only paint
@@ skipping 1735 matching lines @@
 
 LayoutRect LayoutObject::debugRect() const {
   LayoutRect rect;
   LayoutBlock* block = containingBlock();
   if (block)
     block->adjustChildDebugRect(rect);
 
   return rect;
 }
 
+void LayoutObject::invalidatePaintForSelection() {
+  LayoutBlock* block =
+      isLayoutBlock() ? toLayoutBlock(this) : containingBlock();

[mstensho (USE GERRIT), 2017/02/21 21:03:54]

Even if you also explain it in the commit comment, this deserves some
documentation right here, since it's kind of exotic.

So, LayoutBoxModelObject::setSelectionState() sets an accumulated state (start +
end = both) on itself and the containing block chain all the way to LayoutView,
and the code here is a consequence of that, right?

[rune, 2017/02/21 21:42:00]

OK.
Yes.

[rune, 2017/02/21 22:34:57]

Done.

+  if (!block)
+    return;
+  if (!block->hasSelectedChildren())
+    return;
+  for (LayoutObject* child = slowFirstChild(); child;

[mstensho (USE GERRIT), 2017/02/21 21:03:54]

Likewise, I think it's worth mentioning right here why we don't bother to go
deeper than the direct children.

[rune, 2017/02/21 21:42:00]

Acknowledged.

[rune, 2017/02/21 22:34:57]

Done.

+       child = child->nextSibling()) {
+    if (!child->canBeSelectionLeaf())
+      continue;
+    if (child->getSelectionState() == SelectionNone)
+      continue;
+    child->setShouldInvalidateSelection();
+  }
+}
+
 }  // namespace blink
 
 #ifndef NDEBUG
 
 void showTree(const blink::LayoutObject* object) {
   if (object)
     object->showTreeForThis();
   else
     WTFLogAlways("%s", "Cannot showTree. Root is (nil)");
 }
@@ skipping 15 matching lines @@
     const blink::LayoutObject* root = object1;
     while (root->parent())
       root = root->parent();
     root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
   } else {
     WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
   }
 }
 
 #endif